A method for determining the perpendicular distance between an object and a device whose position varies, in particular a motor vehicle, in the case of which method a first sensor which is arranged on this device emits a signal which is reflected by the object, and this reflected signal is received by this first sensor, in which case the delay time of the signal from transmission to reception is used by the first sensor to determine the distance between the first sensor and the object.
In order to make reversing easier, and to prevent collisions with parking vehicles or other objects which are in the way, it is known for sensors to be provided at the rear end of the motor vehicle, which sensors transmit, for example, ultrasound or radar signals and in turn receive the radiation reflected by the obstruction. In this case, the distance between the sensor that is arranged on the motor vehicle and the obstruction is determined from the delay time of the signal from the sensor to the obstruction and back again.
This method has the disadvantage that only one statement can be made about the distance, as such, between the sensor and object. It is not possible, however, to define the perpendicular distance between the obstruction and the motor vehicle (on the basis of the sensor that is arranged on the motor vehicle) owing to the ambiguity resulting from the possible positions of the obstruction that can occur for the same sensor-obstruction distance.
The invention is thus based on the object of specifying a method for determining the perpendicular distance to the object from a motor vehicle.
According to the invention, the object is achieved in that this distance is used to determine all possible positions of the object with respect to the first sensor, the signal reflected by the object is furthermore received by a second sensor, which is likewise arranged on the device whose position varies, and the delay time of the signal from the first sensor to the second sensor is used to determine a path from the first sensor to the object and from this object to the second sensor, from which path all the possible positions of the object with respect to the second sensor are determined, the possible positions of the first sensor and of the second sensor are then compared with one another, and the perpendicular distance to the device whose position varies is calculated for those positions of the object which are determined both by the first sensor and by the second sensor.
The advantage of the invention is that, in addition to reliable determination of the perpendicular distance, it is possible to distinguish reliably between imaginary and real obstructions on the basis of the additional information from the indirect measurement.
In a development, the second sensor transmits a signal which is reflected by the object, and receives this reflected signal (direct measurement), in which case the delay time of this signal is used to determine the possible positions of the object at the same distance from the second sensor.
A real obstruction exists only where all the direct and indirect measurements indicate the position of an object.
In a refinement, all the possible positions of the object with respect to the second sensor are first of all determined in a direct measurement, and the path between the first sensor, the object and the second sensor is then determined in an indirect measurement.
In order to suppress ambiguities, the perpendicular distance between the object and the device whose position varies is determined for that position of the object which was detected both by the indirect measurement by the first sensor and by the direct and indirect measurement by the second sensor.
In order to filter out environmental influences, the distance between the object and the device whose position varies is determined only when the object is located in a sensor corridor which extends between the first sensor and the second sensor.
In a development, when the device whose position varies has a plurality of sensors, the direct and indirect measurement is always carried out by two sensors, and the possible positions of the object determined in this way are compared with one another. The sensor corridor in this case extends between the sensors which are carrying out the present measurement.
Since the sensors are at different distances from one another, sensor corridors of different widths are created when the sensor measurements are carried out in pairs. It is thus possible to locate objects and obstructions in different positions.
If a number of objects at different distances from the device whose position varies are detected, the object at the minimum distance is determined, and the minimum perpendicular distance is calculated and stored.
In a development, the minimum distance to the object is compared with the minimum direct distance to the object detected by an side-edge sensor, and the smaller of these two distances is defined as the minimum distance to the closest object. This also covers the areas beyond the side-edge sensors, which are not covered by the sensor corridors.
In order to detect only obstructions which are actually present, each delay-time measurement is carried out more than once, and a detected object is considered further only if it has been detected in all the measurements. All the sensors must have transmitted a signal once before each first indirect measurement.